DESCRIPTION: HIV infection in combination with opiate drug addiction is an emerging and growing problem, partly due to a longer life expectancy afforded by HAART. Despite effective anti-retroviral therapy (ART) and extended longevity, opiate use exacerbates neurological abnormalities in HIV-infected patients. Our long-term goal is to ameliorate or reverse development of neurological abnormalities that arise despite ART in drug-addicted HIV-infected individuals. The purpose of this R21/R33 proposal is to verify and determine the contribution of perivascular macrophages (PVM) to the virus reservoir in the CNS of SIV-infected macaques following ART and to test if opiate addiction modifies the function of immune cell subsets, including PVM, to fuel the virus reservoir and exacerbate pathogenesis of SIV infection. Our central hypothesis is that long-lived PVM not only serve as major SIV reservoirs but also influence the establishment of virus reservoirs in other cells subsets of the CNS such as microglia and astrocytes in opioid-addicted macaques. To test this, we propose that in vivo depletion of long-lived PVM will reduce or eliminate the virus reservoir and consequently ameliorate the progression of neuropathology and neuroinflammation. The rationale for our hypothesis is that, (i) morphine- dependent SIV-infected macaques display exacerbation of neurological abnormalities observed in parallel in HIV-infected and addicted humans, (ii) reservoir sites of SIV can be examined in finer detail and under more controlled experimental conditions in macaques than in HIV-infected humans, and (iii) we established a safe protocol to eliminate PVM in vivo that will enable us to directly demonstrate their role in the virus reservoir and neuropathogenesis. We propose two aims in phase I (R21) of this application: Aim 1. Determine the effect of morphine on the size and host cell range of the CNS virus reservoir in SIV-infected macaques undergoing ART. Our working hypothesis is that morphine- treated SIV-infected macaques will develop a higher virus reservoir level in PVM and a higher monocyte turnover (indicative of disease progression) than in the SIV-infected-only group at the initiation of ART treatment. Aim 2. Define the specific contribution of PVM to the CNS viral reservoir in opioid-dependent SIV-infected macaques undergoing suppressive ART. Our working hypothesis is that in vivo depletion of PVM will reduce or eliminate the brain virus reservoir in morphine-treated SIV-infected macaques undergoing suppressive ART. To test this, SIV-infected macaques will begin ART after reaching virus set point. The PVM then will be selectively depleted via intrathecal liposomal bisphosphonate (BP) treatment that is expected to induce repopulation by recruiting fresh cells. This approach will also bring to light the magnitude of other cell types that may contribute to the SIV reservoir, such as microglia and astrocytes. These results will demonstrate cellular site(s) and magnitude of SIV reservoirs in the brain of morphine-treated SIV-infected rhesus macaques. Specifically, the outcomes will provide proof-of-concept for the in vivo depletion of PVM and their contribution to the virus reservoir that will lead to testing a treatment strategy targeting PVM to reduce disease progression. This will set the foundation for stud- ies in aim 3 of phase II (R33) to corroborate if targeting PVM earlier after infection and ART will re- duce or ameliorate exacerbation of CNS pathogenesis in morphine-treated SIV-infected macaques. Aim 3. Determine if early in vivo depletion of PVM prevents progression of neuropathogesis in opioid-dependent SIV-infected macaques undergoing suppressive ART. Our working hypothesis is that PVM serve as SIV reservoirs and/or promote development of reservoirs in other host cells. Here, we will determine if in vivo elimination of PVM early after initiating ART will control or re- duce progression of CNS pathogenesis in SIV-infected macaques with chronic morphine treatment. If successful, this study will lead to developing novel therapeutic strategies to effectively target persistent HIV infection of the brain and reverse HAND development.